IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specification for implementing wireless local area network (WLAN) communication, which is also known as Wi-Fi, in the unlicensed (2.4, 3.6, 5, and 60 GHz) frequency bands. The standards and amendments provide the basis for wireless network products using the Wi-Fi frequency bands.
According to the standards, an association identity (AID) is a value assigned by an access point (AP) to represent a 16-bit ID of a station (STA), and a basic service set identification (BSSID) is a 48-bit field of the same format as an IEEE 802 MAC address. The AID is used to identify a STA and the BSSID is used to identify a basic service set (BSS). Since AID and BSSID are inserted into the MAC header or as a management element and therefore belongs to data portion of a packet, they are mostly modulated by high modulation and coding scheme (MCS). Therefore, whether AID and BSSID are correctly received can only be found out until the whole packet is decoded. If a STA receives a packet that is not destined to itself, which means the STA is not the destination of the received packet, the STA needs to decode the whole packet to know it. In many cases, a STA wastes a lot of power decoding packets that are not sent to itself.
To avoid or reduce the frequency of unnecessary decoding of the whole packet, partial AID is introduced in the IEEE 802.11ac standard. A system based on IEEE 802.11ac standard is known as Very High Throughput (VHT) system. IEEE 802.11ac also introduce Partial AID that is a non-unique STA ID assigned by AP or STA. Partial AID is included in VHT_SIG-A1 symbol (the first symbol of VHT-SIG-A symbols), as shown in FIG. 1.
Because VHT-SIG-A symbols are Pre-VHT-modulated fields and include an 8-bit CRC check, the symbols can be easily decoded. When a STA receives a VHT (Very High Throughput) PLCP (PHY Layer Convergence Procedure) protocol data unit (PPDU) with a format shown in FIG. 2, it can determine whether the PPDU is sent to itself or another STA by checking the partial AID after decoding the VHT SIG-A. If the PPDU is not for itself, the STA can turn off receiver for the rest of the PPDU or discard the rest of the PPDU to save power.
In VHT WLAN, the partial AID is defined as shown in Table 1.
TABLE 1ConditionGROUP_IDPARTIAL_AIDAddressed to AP0BSSID[39:47]Addressed to Mesh STA0RA[39:47]Sent by an AP and63 (dec(AID[0:8]) + dec(BSSID[44:47] ⊕ BSSID[40:43])addressed to a STA (9-8a) × 25) mod 29associated with that AP orwheresent by a DLS or TDLS⊕ is a bitwise exclusive OR operationSTA in a direct path to amod X indicates the X-modulo operationDLS or TDLS peer STAdec(A[b:c]) is the cast to decimal operator where b is scaled by20 and c by 2c−bOtherwise (see NOTE)630NOTEThe last row covers the following cases:A PPDU sent to an IBSS STAA PPDU sent by an AP to a non associated STAAny other condition not explicitly listed elsewhere in the table
The Group ID is 0 or 63 to indicate the PPDU is for single user (SU) transmission. For an infrastructure BSS, the Group ID is set to 0 to indicate an uplink transmission and to 63 to indicate a downlink transmission.
In dense networks with overlapped BSS (OBSS), a tradeoff between receive sensitivity and spatial reuse should be considered. In current WLAN, when a STA receives a packet on its primary channel, the STA decodes the pre-VHT-modulation parts and backs off for at least the duration of the received packet. However, this reduces the chance to perform spatial reuse because if the packet is from OBSS, the STA may still be able to transmit if the received packet from OBSS is below a certain signal strength level, e.g., a given clear channel assessment (CCA) level. On the other hand, if the packet is from its own BSS, the STA shall back off even if the signal strength is low.
In VHT WLAN, uplink traffic can be identified using partial AID since it is basically partial BSSID. Contrarily, in current WLAN based on IEEE 802.11a/b/g/n/ac standards, there's no feasible way to identify whether the downlink traffic (AP to non-AP STAs) is from its own BSS or from OBSS and therefore spatial reuse opportunities are reduced.
It is desirable to have a solution to increase the chance to perform spatial reuse VHT stations.